A fish tape is an elongated wire or nonconductive flexible rod typically used to install wire in conduit or through existing walls. Because typical electrical wire is very flexible, pushing it through long lengths of conduit is virtually impossible. Pulling wire through the conduit is much more effective. However, a pulling device such as a fish tape must be stiff enough to be pushed through conduit, flexible enough to negotiate bends or turns in the conduit, and strong enough to pull multiple wires back through the conduit without breaking or separating from the wire being pulled.
Generally, a fish tape is made of steel or fiberglass with a bent loop or metal ferrule on one end for attaching to the electrical wire that is pulled through the conduit. On steel fish tape, a loop can be bent in the end or, if a ferrule is used it can be attached by various means such as welding or a threaded attachment. These attachment methods, however are not available for fiberglass fish tapes. Welding will melt fiberglass. A threaded connection would cut into the protective skin of the fiberglass damaging the fiberglass integrity and causing the ferrule to separate prematurely from the fish tape. Thus the use of attachment methods effective on steel fish tapes are not effective with fiberglass fish tapes.
Prior art methods for attaching a ferrule to the end of a fiberglass fish tape typically employ a friction connection. One method to attach a ferrule to a fiberglass rod is to crimp the ferrule onto a plastic jacket coating the fiberglass rod, being careful not to damage the fiberglass. Another method is to join the fiberglass rod with a ferrule having a smooth socket interior using an adhesive. This method does not damage the fiberglass rod, but the strength of the connection is still essentially only a friction fit because the adhesive does not bond well to a metallic surface.
Still another method of attaching a nonmetallic fish tape to a ferrule, as disclosed in U.S. Pat. No. 3,858,848, MacFetrich, issued Jan. 7, 1995, is to insert the fish tape into a tubular ferrule having external threads and a portion of its bore conical. The fish tape is then expanded in the conical part of the ferrule bore by threadably inserting a screw into the end of the tape. The expanded tape creates a taper-lock connection with the ferrule. The ferrule is then threadably connected to a head having internal threads.
Continuous use of a fiberglass fish tape employing such a fit to connect the ferrule to the tape end results in the eventual loosening of the connection and separation of the ferrule from the tape. In addition, exerting too much pulling force when pulling wire through a conduit connected to the ferrule may also result in over compression of the end of the fish tape and therefore a separation between the tape and ferrule. Therefore, it is desirable to have a ferrule connecting method and apparatus that does not loosen over time and can withstand a greater pulling force than is currently available in the art.